This error is mostly likely caused indirectly by has_many through, which requires an id column to be present in the join table in a many-to-many relationship:

ActiveRecord::StatementInvalid: Mysql::Error: Unknown column 'id' in 'where clause': DELETE FROM brand_posts WHERE id = NULL

The fix is to create the id column, which in this case is done like this:

add_column :brand_posts, :id, :primary_key